In outboard motors, the engine is covered with an engine cover that is composed of an upper cover and a lower cover. An external air inlet and a discharge outlet are formed in the engine cover, and the inside of the engine cover (e.g., engine room) is ventilated by driving a ventilation fan that is attached to the end of a crank shaft (refer to JP-A-1-271610 and JP-A-4-166496, for example).
JP-A-1-271610 and JP-A-4-166496 disclose outboard motors in which an external air inlet and a discharge outlet are formed in an upper cover and a ventilation fan is disposed at a top end of the engine. While the ventilation fan is driven, air that is introduced through the external air inlet moves inside an engine room and is discharged through the discharge outlet.